172 BYZANTINE CHURCHES CHAP.
with the ground outside the church, stone steps are employed for the remainder of the way up. The wooden steps are Turkish, but may replace Byzantine steps of the same material. The stone steps are Byzantine, and could be reached directly from outside the church through the door situated • beside the landing from which they start. Probably in Byzantine days the stone staircase could not be reached from the floor of the church, and furnished the only means of access to the galleries.
The galleries are covered by the barrel vaults of the cross arms. At the east end of the northern and the southern gallery are chapels covered with domes and placed above the prothesis and the diaconicon. As stated already, the aperture In the roof of the chamber in the south-eastern dome pier opens into the floor of the southern chapel, and probably a similar aperture in the roof of the corresponding chamber in the north-eastern pier opened into the floor of the chapel at the east end of .the northern gallery. The presence of chapels in such an unusual position is explained by the desire to celebrate special services in honour of the saints whose remains were buried in the chambers in the piers, as though in crypts.
The domes over the chapels are hemispherical and rest directly on the pendentives. They are ribless and without drums. The arches on which they rest are semicircular and, with their infilling of triple windows, are Byzantine. We may safely set down all four angle domes as belonging to the original design, though the arches by which they communicate with the galleries are pointed, and are therefore Turkish insertions or enlargements.
On the exterior the eastern wall of the church is fairly well preserved. The three apses project boldly ; the central apse in seven sides, the lateral apses in three sides. Although the central apse is unquestionably a piece of Byzantine work it does not appear to be the original apse of the building, but a substitute inserted in the course of repairs before the Turkish conquest. This accounts for its plain appearance as compared with the lateral apses, which are decorated with four tiers of five niches, corre-